Enhanced Mechanical Properties and Corrosion Behavior of Zn–30Sn–2Cu High-Temperature Lead-Free Solder Alloy by Adding Sm

Zn–30Sn–2Cu–xSm (x = 0, 0.1, 0.3, 0.5, and 1.0 wt%) solders were prepared to investigate its mechanical properties and corrosion behavior. With the addition of 0.3 wt% Sm, the ultimate tensile strength reached the highest level of 98.6 MPa. The fracture morphology transitioned from ductile fracture to mixed ductile–brittle fracture. The corrosion behaviors of Zn–30Sn–2Cu, including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), were researched with the introduction of Sm. The Sm addition could modify the microstructure of alloy in terms of the size and distribution of Zn-rich phase. Meanwhile, the finer and more uniform corrosion product formed on the surface of alloys was contributed to the addition of Sm. With Sm content further reaching 5 wt %, the galvanic corrosion occurred between the newly formed Sm1.11Zn11.77 IMC and Zn phase, accelerating the dissolution of Zn phase which is harmful to its corrosion resistance. In addition, the results of electrochemical measurement showed that Zn–30Sn–2Cu–0.5Sm alloy had the lowest value of corrosion current density (4.11 μA cm−2) and the highest value of total resistance (2608 Ω cm2). Thus Zn–30Sn–2Cu–0.5Sm alloy possessed the most excellent corrosion resistance.